The subject disclosure relates to superconducting devices, and more specifically, to fabricating a vertical Josephson junction superconducting device using a silicon-on-metal (SOM) substrate.
Quantum computing is generally the use of quantum-mechanical phenomena for the purpose of performing computing and information processing functions. Quantum computing can be viewed in contrast to classical computing, which generally operates on binary values with transistors. That is, while classical computers can operate on bit values that are either 0 or 1, quantum computers operate on quantum bits that comprise superpositions of both 0 and 1, can entangle multiple quantum bits, and use interference to obtain computational results.
Quantum computing hardware can be different from classical computing hardware. In particular, superconducting quantum circuits generally rely on Josephson junctions, which can be fabricated in a semiconductor device. A Josephson junction generally manifests the Josephson effect of a supercurrent, where current can flow indefinitely across a Josephson junction without an applied voltage. A Josephson junction can be created by weakly coupling two superconductors (a material that conducts electricity without resistance), for example, by a tunnel barrier as described below.
Some prior art Josephson junctions can be implemented using shadow evaporation. A problem with fabricating prior art Josephson junctions using shadow evaporation can be that this approach is not scalable, because shadow evaporation can produce non-uniform results on larger substrates, such as 200 mm or 300 mm wafers. Josephson junctions implemented via shadow evaporation can have high variability of the supercurrent. Josephson junctions implemented via shadow evaporation can be made with a lift-off process, which, in turn, can cause flares at the edges of a remaining superconducting layer, can allow for one or more floating superconducting islands to be formed near a Josephson junction (where using undercut in resist, or hard mask, profile); and can have some junction variability (which causes variability of the critical current) caused by undercut and small misalignments in tilted evaporation. Additionally, a problem with shadow evaporation is that a number of choices for both materials and deposition approaches can be limited.
There are also Josephson junctions used in single flux quantum (SFQ) computing, which can be vertical, but can have a problem of having an associated loss beyond what is suitable for quantum computing. This associated loss with a SFQ junction can include both loss due to surrounding dielectrics with insufficient loss tangent, and loss in tunnel barrier. Additionally, a SFQ junction generally has a larger area than a quantum bit (qubit) junction.